Kyounghoon Lee

Development of a low-energy used large midwater trawl using a numerical method

Fuel consumption in fisheries is a primary concern due to environmental effects and costs to fishermen. Much research has been carried out to reduce the fuel consumption related to fishing operations. The fuel consumption of fishing gear during fishing operation is generally related to hydrodynamic resistance on the gear. This research demonstrates a new approach using numerical methods to reduce fuel consumption. The results from the simulation were verified with results that mirrored the model experiments. By designing the fishing gear using drawing software, the whole and partial resistance force on the gear can be calculated as a result of simulations. The simulation results will suggest suitable materials or gear structure for reducing the hydrodynamic forces on the gear while maintaining the performance of the gear. Furthermore, the efficiency of low energy used trawl as economic point of view will be dealt. This research will helpful to reduce the GHG emissions from fishing operations and lead to reduce fishing costs due to fuel savings.

Measurement of swimming ability of moon jellyfish using a particle imaging velocimetry

The swimming behavior and biomimetics of marine organisms have been recently investigated to understand the interrelation between the organism and the fluid in the fluid dynamics by using a variety of digital optic instrument technologies. Unlike the terrestrial animals, the marine organisms were biologically evolved and developed in hydrodynamic so that they have a linear structure suitable to high pressures and strong tidal currents as well as propulsion feature for moving. It has been known that the jellyfish would have a swimming ability to utilize the kinetic energy effectively during swimming. This study is aimed to investigate and analyze characteristics of vortex wave formation and vorticity structure of both side of moon jellyfishs bell with oblate-shaped which was changed by width-to-height ratio rowing in swimming by using 2 dimensional analysis in PIV (Particle Image Velocimetry) method. Results showed that the ratio of height-to-width (W/H) was ranged in 0.3–0.6 and the swimming speed was estimated to be slow at 0.5 of W/H. When it turns, the 2D bell of a moon jellyfish was shown in rowing at 0.5— 0.6 and there is no propulsion without rowing under 0.5 at W/H ratio. Also this result has shown that the jellyfish moved to the left side from the central axis, the right side of the vortical structure of the bell had a faster speed, and its propulsion was obtained from the movement of the central axis resulting from the difference between the speeds of the left and right sides of the bell.

Acoustic monitoring using multi-beam imaging sonar through a set net in the Southern Sea, Korea

This study investigated a method for monitoring fish flux though a set net in the coastal South Sea, Korea, using sideward-looking wide angle multi-beam imaging sonar (blueview). This data set was used to examine the impact of changes in diel variation and current speed from a set net. During nighttime, the influx of fish in the set net was significantly 22 times higher than in daytime. The time when high fish flux was observed corresponded to the time of low current speed during nighttime. In contrast, the fish flux was not affecting current speed during daytime. The study provides implications for understanding fish behavior through use of a set net.

AB0758 The Relationships between Bone Mineral Density and Radiographic Features of Hand or Knee Osteoarthritis in Older Adults: Data from The Dong-Gu Study

Objectives The relationship between osteoarthritis (OA) and osteoporosis has exhibited contradictory features over the past four decades. The aim of this study was to evaluate this relationship using separate analysis of the radiographic features of OA whether various radiographic features of OA were associated differently with bone mineral density (BMD) in the Korean elderly. Methods Data were derived from the Dong-gu cohort; 2,354 subjects were enrolled in the present cross-sectional study. Baseline characteristics, the BMDs of the lumbar spine and femoral neck which was measured by DXA, and X-rays of knees and hands, were collected. A semi-quantitative grading system was used to estimate the severities of individual radiographic features. We adjusted for confounders using multiple linear regression modeling to analyze the relationships. Results After adjustment for confounders, hand and knee OA total scores were negatively associated with the BMDs of the lumbar spine and femoral neck, except for the total knee OA score and lumbar spine BMD. In detail, hand osteophytes and sclerosis exhibited positive relationships with the BMDs of the lumbar spine and femoral neck, except for hand osteophytes and femoral neck BMD. On the contrary, however, knee joint space narrowing (JSN), hand JSN, and hand subchondral cysts were negatively associated with the BMD of the lumbar spine and femoral neck. Knee JSN and hand subchondral cysts exerted the greatest effects on BMD. Conclusions Separate analysis of the radiographic features of OA better reveals associations of OA with the BMD of the lumbar spine and femoral neck. Disclosure of Interest None declared

Behavior and Frequency Analysis of Aurelia aurita by Using in situ Target Strength at a Port in Southwestern Korea

This study was carried out to determine the in situ target strength and behavioral characteristics of moon jellyfish (Aurelia aurita) using two frequencies (38 and 120 kHz) that present a 2- frequency-difference method for distinguishing A. aurita from other marine planktonic organisms. The average TS was shown as -71.9~ -67.9 dB at 38 kHz and -75.5~-66.0 dB at 120 kHz and the average ΔMVBS120-38 kHz was similar at -1.5~3.5 dB. The TS values varied in a range of about 14 dB from -83.3 and -69.0 dB depending on the pulsation of A. aurita. The species moved in a range of -0.1~1.0 m and they mostly moved horizontally with moving speeds of 0.3~0.6 m·s-1. The TS and behavioral characteristics of A. aurita can distinguish the species from others. The acoustic technology can also contribute to understanding the distribution and abundance of the species.

Target-strength Measurements of Sandfish Arctoscopus japonicus

The goal of this study was to estimate the target strength (TS) of the sandfish Arctoscopus japonicus using in-situ and ex-situ methods with an echosounder. For the in-situ TS measurement, the survey was conducted by taking hydroacoustic measurements at 38 and 120 kHz and using a coastal gill net, in Goseong, in the northeastern sea of Korea in early December 2009. Ex-situ measurement of TS used live specimens and the tethering method, and was conducted at 120 kHz. The distribution of fork length (FL) was bimodal: 14.6–19.8 cm (n = 241 individuals, mean = 17.0 cm) for males and 16.3–24.5 cm (n = 105 individuals, mean = 19.6 cm) for females. The in-situ TS ranged from −79.8 to −59.1 dB (mean = −74.3 dB for males and −64.1 dB for females) at 38 kHz and −79.9 to −56.2 dB (mean = −74.3 dB for males and −64.1 dB for females) at 120 kHz. The mean TS of females was approximately 10 dB higher than that of males at each dominant frequency. The female ex-situ TS values ranged from 68.5 to −54.6 dB, and those of males was from −67.7 to −59.3 dB. The mean TS value for females was 2.9 dB higher than that of males. These results may be used in echo-integration surveys of sandfish to estimate their abundance and seasonal distribution.

Characterization of Frequency and Aggregation of the Antarctic Krill (Euphausia superba) Using Acoustics

In this study, the dB difference and characteristics of krill swarms inhabiting Subarea 48.1, which includes the west and south of the South Shetland Island and the Elephant Island peripheries, were estimated to distinguish Antarctic krill, using acoustics. From April 13 to 24, 2016, acoustic data were collected along 24 survey lines using the frequencies 38 and 120 kHz, and middle trawling was performed at 7 stations. Using the difference between the dB values of two volume backscattering strength (Sv) frequencies (38 and 120 kHz), a clear acoustic distinction could be made between Antarctic krill (4.9 to 12.0 dB) and fish (−4.0 to −0.2 dB). The distributions and mean Sv of krill swarms in the Elephant Island peripheries and south of South Shetland Island were higher than those in the west of South Shetland Island. The mean length/ height ratio of krill swarms in the west of the South Shetland Island (64.5) was higher than that in the south (35.9) and the Elephant Island peripheries (33.8), with the length of the aggregations exceeding their height. Most krill swarms were distributed between the surface layer (less than 10 m below sea level) and within 200 m of water depth. These results are expected to serve as baseline data for evaluating krill density and biomass by distinguishing them from fish, using acoustics.

Behavioral patterns and in-situ target strength of the hairtail ( Trichiurus lepturus ) via coupling of scientific echosounder and acoustic camera data

The present study focuses on the influence of target strength (TS) changes in the swimming angle of the hairtail (Trichiurus lepturus). We measured in-situ TS at 38 and 120 kHz with luring lamps at a fishing ground for jigging boats near the coastal waters of Jeju-do in Korea. Swimming angle and size of hairtails were measured using an acoustic camera. Results showed that mean preanal length was estimated to be 13.5 cm (SD = 2.7 cm) and mean swimming tilt angle was estimated to be 43.9° (SD = 17.6°). The mean TS values were −35.7 and −41.2 dB at 38 and 120 kHz, respectively. The results will assist in understanding the influence of swimming angle on the TS of hairtails and, thus, improve the accuracy of biomass estimates.

Acoustic monitoring using bamboo set net in the Southern Sea of Korea

High-temporal resolution profiles of acoustic backscatter were collected from a traditional bamboo set net along the coast of the Southern Sea, Korea, using sideward-looking multi-beam imaging sonar. These data were used to examine the impact of variations in tidal cycles and current speeds on the bamboo set net. The relatively high influx of fish during the nighttime compared to the low influx and high outflux of fish during the daytime suggests visual avoidance of the net by the fish during the daytime. The observed diel variation in the captured fish flux was significantly correlated with the current speed (day: r = 0.35, p = 0.002, night: r = 0.60, p < 0.001). The ratio of influx and outflux of fish, and current speed were correlated in a linear relationship (day: r = 0.45, p < 0.001; night: r = 0.56, p < 0.001). The fish activity of those inhabiting the bamboo set nets appears to be greatly influenced by day-night differences and current speed. The present study enhances understanding of fish behavior via utilization of a bamboo set net in the coastal zone.

Vertical distribution of giant jellyfish, Nemopilema nomurai using acoustics and optics

Nemopilema nomurai jellyfish, which are believed to complete their development in the East China Sea, have started migrating into the Yellow Sea in recent years. We obtained biomass estimates of this species in the Yellow Sea using bottom trawl fishing gear and sighting surveys over a 5-year period. These methods are effective for obtaining N. nomurai jellyfish density estimates and information about the community distribution near the bottom or surface of the sea. To verify the vertical distributions of giant jellyfish between, we used hydroacoustic equipment, including an optical stereo camera system attached to a towed sledge and an echo counting method with scientific echosounder system. Acoustic and optical data were collected while the vessel moved at 3 knots, from which the distribution and density of N. nomurai jellyfish were analyzed. Subsequently, the camera system was towed from a 7 m mean depth to sea level, with the detection range of the acoustic system extending from an 8 m depth to the bottom surface. The optical and acoustic methods indicated the presence of vertical distribution of 0.113 (inds/m3) and 0.064 (inds/m3), respectively. However, the vertical distribution indicated that around 93% of individuals occurred at a depth range of 10–40 m; thus, a 2.4-fold greater density was estimated by acoustic echo counting compared to the optical method.